The spinal column consists of thirty-three bones called vertebra, the first twenty-four vertebrae of which make up the cervical, thoracic, and lumbar regions of the spine and are separated from each other by “pads” of tough cartilage called “intervertebral discs,” which act as shock absorbers that provide flexibility, stability, and pain-free movement of the spine.
FIGS. 1 and 2 illustrate a portion of a healthy and normal spine, and specifically, two vertebra 10 and two intervertebral discs 12 (only one shown). The posterior of the vertebra 10 includes right and left transverse processes 14R, 14L, right and left superior articular processes 16R, 16L, and a spinous process 18. Muscles and ligaments that move and stabilize the vertebra 10 are connected to these structures. The vertebra 10 further includes a centrally located lamina 20 with right and left lamina 20R, 20L, that lie inbetween the spinous process 18 and the superior articular processes 16R, 16L. Right and left pedicles 22R, 22L are positioned anterior to the right and left transverse processes 14R, 14L, respectively. A vertebral arch 24 extends between the pedicles 22 and through the lamina 20. The anterior of the vertebra 10 includes a vertebral body 26, which joins the vertebral arch 24 at the pedicles 22. The vertebral body 26 includes an interior volume of reticulated, cancellous bone (not shown) enclosed by a compact cortical bone 30 around the exterior. The vertebral arch 24 and vertebral body 26 make up the spinal canal (i.e., the vertebral foramen 32), which is the opening through which the spinal cord 34 and epidural veins (not shown) pass. Nerve roots 36 laterally pass from the spinal cord 34 out through canals 38 in the side of the spinal column formed between the pedicles 22. Structurally, the intervertebral disc 12 consists of two parts: an inner gel-like nucleus (nucleus pulposis) 40 located at the center of the disc 12, and tough fibrus outer annulus (annulus fibrosis) 42 surrounding the nucleus 40.
A person may develop any one of a variety of debilitating spinal conditions and diseases. For example, as illustrated in FIG. 3, when the outer wall of the disc 12′ (i.e., the annulus fibrosis 42) becomes weakened through age or injury, it may tear allowing the soft inner part of the disc 12 (i.e., the nucleus pulposis 40) to bulge out, forming a hernia 46. The herniated disc 12′ often pinches or compresses the adjacent dorsal root 36 against a portion of the vertebra 10, resulting in weakness, tingling, numbness, or pain in the back, legs or arm areas.
Often, inflammation from disc herniation can be treated successfully by nonsurgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosterioids. In some cases, however, the disc tissue is irreparably damaged, in which case, surgery is the best option.
Discectomy, which involves removing all, or a portion, of the affected disc, is the most common surgical treatment for ruptured or herniated discs of the lumbar spine. In most cases, a laminectomy procedure is performed by removing at least a portion of the lamina in order to visualize the affected disc. Once the vertebrae, disc, and other surrounding structures can be visualized, the surgeon will remove the section of the disc that is protruding from the disc wall and any other disc fragments that may have been expelled from the disc. In some cases, the entire disc may be removed.
Besides disc hernias, other debilitating spinal conditions or diseases may occur. For example, spinal stenosis, which results from new bone and soft tissue growth on a vertebra, reduces the space within the spinal canal. When the nerve roots are pinched, a painful, burning, tingling, and/or numbing sensation is felt down the lower back, down legs, and sometimes in the feet. As illustrated in FIG. 2, the spinal canal 32 has a rounded triangular shape that holds the spinal cord 34 without pinching. The nerve roots 36 leave the spinal canal 32 through the nerve root canals 38, which should be free of obstruction. As shown in FIG. 4, new bone growth 48 (e.g., bone spurs) within the spinal canal 32, and specifically from the diseased lamina 20, causes compression of the nerve roots, which leads to the pain of spinal stenosis. Spinal stenosis may be treated by performing a laminectomy in order to relieve pressure on the nerve root 36 impinged by the bone growth 48. Along with the laminectomy, a foraminotomy, (i.e., enlarging of the channel from which the nerve roots 36 exit is performed). Depending on the extent of the bone growth, the entire lamina and spinal process may be removed.
Thus, it can be appreciated that in many spinal treatment procedures, bone and/or disc tissue must be removed in order to release pressure from neural tissue or rebuild the vertebra. In the case of target bone tissue that is adjacent spinal tissue, a physician is required to exercise extreme care when cutting away the target bone tissue (e.g., during a laminectomy and foraminotomy), such that injury to spinal tissue can be prevented. A physician may have difficulty controlling existing bone removal devices, however, and may unintentionally remove healthy bone tissue or injure spinal tissue during use. This problem is exacerbated with percutaneous treatments, which, although less invasive than other procedures, limit the range of motion of the cutting instrument, thereby further limiting the control that the physician may have during the bone cutting procedure.
For example, when removing target tissue at the lamina 20 (e.g., tissue of the bone growth 48), a burr-type tissue removal probe 70 can be inserted through a patient's skin 62 such that a burr 74 at a distal end 72 of the probe 70 can make contact with the target tissue. The tissue removal probe 70 is then positioned back and forth (as indicated by arrows 80, 82) to remove the target tissue, thereby creating a channel to relieve pressure on the nerve root 36 impinged by the bone growth 48. However, because of the close proximity between the burr 74 and the nerve root 36, there is a significant risk that the burr 74, if improperly positioned, may accidentally injure the nerve root 36 during such procedure. In addition, the movement of the distal end 72 of the probe 70 may cause the probe 70 to rub or abrade against the nerve root 36, thereby injuring the nerve root 36.
There, thus, remains a need to provide for tissue removal device and methods for removing tissue targeted for removal, while minimizing injury to non-target tissue.